The invention relates to an improved excimer lamp of the type with a discharge chamber usually of quartz or ceramic, and which holds a halogen-containing filling gas forming excimers under discharge conditions. The invention also relates to a method for the manufacture of a long-life excimer lamp; a method for extending the burning life of such an excimer lamp; and a device for practicing the latter method.
Excimer lamps are used for generating high-energy ultraviolet radiation. The excimer radiation is also described as silent electrical discharge. This is generated in a discharge chamber bound by dielectrics in which the filling gas forming the excimers is contained.
An excimer lamp of the specified type is known from EP-A1 0 547 366. In the excimer lamp described therein, a variety of noble gases are proposed as filling gases depending on the desired spectral composition of the radiation, for example, argon, krypton or xenon or noble gas mixtures, respectively, which, for example, contain chlorine or a chlorine-containing compound from which one or more chlorine atoms are expelled during the discharge.
No indications are given in EP-A1 547 366 as to the chlorine concentration to be used. In excimer lamps commercially available currently, the chlorine content is based on the chlorine content of the corresponding excimer lasers at a mixing ratio of chlorine to a noble gas or a noble gas mixture, respectively, of 1/1000. An excimer lamp of this type, for example, is described in the dissertation by Mr. Volker Shorpp entitled "The Dielectrically Inhibited Noble Gas-Halogen-Excimer Discharge: A New Type of Ultraviolet Radiation Source," University of Karlsruhe, 1991.
From EP-A2 0 521 553 an excimer lamp is known which is developed as a planar flatform lamp. The discharge chamber contains a halogen-containing noble gas filling, whereby the partial pressure of the halogen is between 0.05% and 5% of the partial pressure of the noble gas. The known excimer lamp is characterized by a high radiation intensity.
In excimer lamps known until now, the maximally adjustable ultraviolet radiation intensity already decreases within the first 300 hours of operation. The drop in the ultraviolet radiation intensity is typically greater than 50% of the initial radiation intensity.
An attempt to extend the burning life of a lamp of this type is described in EP-A1 607 960. Therein an excimer lamp is described which features a discharge chamber which is sealed in a gas-proof fashion and is filled with a suitable filling gas. In order to extend the burning life of the lamp, EP-A 1607960 teaches the proposed elimination of gaseous impurities in the filling gas and to that end provide a "getter" which may be disposed inside the discharge chamber or in connection with it. However, it has been demonstrated that eliminating filling gas impurities is not sufficient for a marked increase in-burning life.
It is therefore an object of the present invention to provide an excimer lamp with a long burning life as well as to provide a method for manufacturing such an excimer lamp. A further object of the invention is to provide a method for extending the burning life of excimer lamps and a device suitable to practice this method.